A typical roller cone earth-boring bit has a bit body with three bit legs. A bearing pin extends from each bit leg, and a cone rotatably mounts on the bearing pin. The bearing surfaces between the cavity of the cone and the bearing pin are filled with a lubricant. A seal is located between the cone and the bearing pin to seal lubricant within and keep drilling fluid from entry.
Many designs for seals have been proposed and used. One type comprises an elastomeric ring that is located in a groove in the cone near the mouth of the cavity. The ring normally rotates with the cone and seals against the stationary bearing pin. The ring and seal groove are designed to provide a selected contact pressure of the inner diameter of the ring with the bearing pin. A high downward force is imposed on the drill bit during operation, resulting in a higher contact pressure on the lower side of the bearing pin than on the upper side. Also, during operation, there may be slight cone movement relative to the axis of the bearing pin. This movement results in varying contact pressure on both the bearing and seal. Varying contact pressure can cause excessive heat and wear in certain areas of the seal, shortening the life. Also, cuttings from the earth formation are able to contact portions of the seal and tend to cause it to wear.
U.S. Pat. Nos. 5,005,989, 5,570,750, and 4,934,467 disclose installing a rigid insert ring on the bearing pin for engagement by the inner diameter of the seal ring. The insert ring is of harder material than the bearing pin for reducing wear on the seal ring. In the FIG. 7 embodiment of the '989 patent, the insert ring is located on and fixed relative to the bearing pin by a vulcanized layer.